Cheng Yangchun

Design of induced power apparatus for monitoring system of dynamic increasing capacity of high-voltage transmission lines

This paper uses CT to gain the energy directly from the high-voltage power line, which is to address the problem of power supply for monitoring system of dynamic increasing capacity in high voltage side of transmission line. The draw-out power coil can induce voltage from the transmission line whose current ranges from 50 to 1000A. Then after rectifying, filtering, voltage reduction and voltage stabilization, it can finally output stable DC voltage of +5V. Single-chip microcomputer is selected to calculate secondary sides voltage, and analog output square wave to control the switching transistor, in order to increase the current of the secondary side. The method of adding secondary-side current significantly increases the saturated current of coil. And in a accordance with the theoretical calculation, parameters such as coil structure, core material and winding turns are matched reasonably. The power supply based on this kind of draw-out power coil has undergone the overall testing, and it is verified-showing that it can work in a non-saturated and low-consumed status within the range of normal operating current, and provide a stable output. The equipment has also increased over-voltage protection circuit to avoid the damage of the impulse current or short-circuit current to power supply circuit. It solves the power supply of high voltage side of transmission line.

Breakdown characteristics of CF 3 I and CF 3 I/N 2 gas mixtures in uniform field

With its high insulation capability and excellent environmental friendliness, CF₃I has been considered as a potential substitute to SF₆. However, considering its high boiling point, CF₃I should be mixed with buffer gases such as CO₂ or N₂. In this paper, breakdown performance of CF₃I/N₂ gas mixtures, SF₆/N₂ gas mixtures and pure SF₆ gas in uniform field are investigated, with negative dc voltage or negative lightning impulse voltage applying. DC breakdown experiments of pure CF₃I gas and pure SF₆ gas show that the dielectric strength of CF₃I is not always higher than that of SF₆. The insulation experimental results show that in low pressures, 30%CF₃I/70%N₂ gas mixtures present similar insulation properties as 20%SF₆/80%N₂ gas mixtures. Considering liquefaction temperature and insulation properties, 30%CF₃I/70%N₂ gas mixtures could be possible substitutes to SF₆ or SF₆/N₂ gas mixtures in low pressures, and it is significant to study their insulation strength in higher pressures.